Most energy storage systems exhibit limited capacities despite their use of high energy and low atomic weight materials (e.g. lithium, sodium, magnesium or zinc anode). Batteries with these types of metallic anodes could drastically impact applications that demand a rugged, safety-focused, low weight, small volume, or high energy-density power source. For example, metal-air batteries show great promise as an automobile power source.
Metal-air batteries are batteries which use an anode made from a metal and an external cathode of ambient air (e.g., oxygen) along with an electrolyte and a separator. Importantly, there is a direct relationship between the oxygen solubility in the electrolyte and energy density of a metal-air battery. Despite recent progress in developing metal-air batteries, challenges remain. One such challenge is the choice of a suitable electrolyte. An electrolyte used in a metal-air battery should meet the requirements for reactant (e.g., oxygen) solubility and diffusivity, ionic conductivity, thermal and electrochemically stability and compatibility with electrode materials. Currently, fast transport of the reactant, oxygen, through the electrolyte is a primary obstacle to achieving high performance in metal-air batteries.
Several different types of electrolytes can be used as the electrolyte in a metal-air battery, such as aqueous electrolytes, organic electrolytes, solid-state electrolytes, and ionic liquids. Ionic liquids are useful as an electrolyte component in lithium, sodium, magnesium, and zinc batteries as they are non-volatile, non-flammable, have a low melting point, and have high ionic conductivity.